The present invention relates generally to the manufacture of crepe paper products, and more particularly to a modified creping adhesive composition which facilitates the creping of paper webs for making disposable and/or absorbent tissue, towels, napkins, or other paper products.
Paper is generally manufactured by suspending cellulosic fiber of appropriate geometric dimensions in an aqueous medium, forming the fiber into a wet ribbon or web on a porous support and then drying the web. In the manufacture of disposable and/or absorbent tissue, towel and the like, creping is performed in order to impart desired aesthetic and performance properties to the resulting product. Creping is generally carried out by causing the cellulosic fiber web to adhere to the surface of a large, rotating cylindrical dryer, known in the industry as a Yankee dryer, and then scraping the web off of the dryer surface by means of a doctor blade. This blade is also sometimes referred to as a creping blade. The result is an increase in basis weight (mass per unit area) as well as dramatic changes in many physical properties of the web, particularly when measured in the machine direction.
Traditionally, absorbent paper has been produced by one of three basic technologies: (i) conventional wet press technology with wet creping and embossing, as described in U.S. Pat. No. 5,048,589 to Cook et al.; (ii) conventional wet press technology with dry creping and embossing, as described in U.S. Pat. No. 5,048,589 to Cook et al.; and (iii) through-air-drying (TAD), with or without creping. Conventional TAD processes are generally described in U.S. Pat. No. 3,301,746 to Sanford et al. and U.S. Pat. No. 3,905,863 to Ayers.
Typically, the paper web is first formed on a foraminous carrier or support, such as a Fourdrinier wire, where it is freed of the copious water needed to disperse the fibrous slurry. Thereafter, it is usually transferred to a felt or fabric in a so-called press section where de-watering is continued either by mechanically compacting the paper or by some other de-watering method such as through-drying with hot air, before finally being transferred in the semi-dry condition to the surface of the Yankee dryer for the drying to be completed.
The impact of the adhered web with the doctor blade is essential in order to obtain from the drying process a dried paper web having the properties desired by the manufacturer. This creping action has the effect of breaking a substantial number of interfiber bonds in the paper web, increasing its bulk, and resulting in improved softness and absorbency. The term “bulk,” as used herein, refers to the inverse of the density of a tissue paper web.
The paper web is caused to adhere to the Yankee dryer well around the cylindrical heating surface from the doctor blade, which crepes the traveling web as it is separated from the dryer. To adhere the nascent web to the surface of the Yankee dryer, a creping adhesive alone or in combination with a release agent, ordinarily in the form of an aqueous solution, emulsion or dispersion, is applied to the rotating surface prior to its taking up the partially dried web, which occurs with the assistance of a pressure roll. Alternatively, the spray may be applied to the traveling web. Suitable apparatus for use with the present invention is disclosed in U.S. Pat. No. 4,304,625 to Grube et al. and U.S. Pat. No. 4,064,213 to Lazorisak et al.
The level of adhesion of the papermaking web to the dryer is of considerable importance in relation to control of the web in its travel in the space between the creping blade and the reel, and to crepe formation itself. Different creped products require different levels of adhesion, tack and rewetability. For example, a facial tissue web will require a different level of adhesion and tack and rewetability in comparison to a paper towel web. Webs which are not sufficiently adhered to the dryer tend be difficult to control, with consequent difficulties in forming a uniform reel of paper. A loose sheet leads to poor creping, wrinkles in the reel, Holdovers, or weaving of the sheet in the rolled-up paper, which can lead to problems in converting. Hence it is very important to be able to control the level of adhesion and tack of the adhesive package (i.e., adhesive plus additives) by appropriate modification of its properties.
The level of adhesion of the papermaking web to the drying surface is also of importance in relation to the drying of the web. Higher levels of adhesion tend to promote heat transfer and cause the web to dry faster, enabling more energy efficient, higher speed operation. Low levels of adhesion can inhibit heat transfer, resulting in poor drying of the web.
Rewetability is another important characteristic of a creping adhesive. “Rewetability,” as used herein, refers to the ability of the adhesive material to be activated by the moisture contained in the semi-dry web when the web is brought into contact with the adhesive material on the heated drying surface. A marked increase in tack is indicative of high rewetability.
Various types of creping adhesives are known. Some unmodified adhesives, such as polyamidoamine-epichlorohydrin (PAAE) and polyvinyl alcohol (PVOH) tend to form a very hard coating with poor tack and rewetability properties. It is also known to incorporate one or more modifier into a-creping adhesive to impart certain desirable properties to the adhesive. See, for example, U.S. Pat. No. 6,280,571 to Allen.
The development of a creping adhesive providing enhanced performance with respect to level of adhesion, tack and rewetability remains a highly desired objective in the paper industry.